Control valve timing

ABSTRACT

A method for lifting drilling mud from subsea to a drilling vessel which a pump having a body with a chamber, and a bladder in the chamber. The bladder attaches to the body and defines water and mud sides in the chamber. A mud inlet valve allows mud into the mud side of the chamber; which moves the bladder into the water side and urges water in the water side from the chamber and through a water exit valve. Pressurized water enters the chamber through a water inlet valve, which in turn pushes the bladder and mud from the chamber through a mud exit valve. The bladder separates the mud and water as it reciprocates in the chamber. Water and/or mud inlet valves are opened before associated exit valves to reduce pressure fluctuations in the fluid lines.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of co-pending U.S. Provisional Application Ser. No. 61/792,157, filed Mar. 15, 2013, the full disclosure of which is hereby incorporated by reference herein for all purposes.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present disclosure relates in general to a system and method for timing the opening and closing of inlet and outlet valves used with a bladder pump to reduce pressure spikes within the pump.

2. Description of Prior Art

Subsea drilling systems typically employ a vessel at the sea surface, a riser connecting the vessel with a wellhead housing on the seafloor, and a drill string. A drill bit is attached on a lower end of the drill string, and used for excavating a borehole through the formation below the seafloor. The drill string is suspended subsea from the vessel into the riser, and is protected from seawater while inside of the riser. Past the lower end of the riser, the drill string inserts through the wellhead housing just above where it contacts the formation. Generally, a rotary table or top drive is provided on the vessel for rotating the string and bit. Drilling mud is usually pumped under pressure into the drill string, and is discharged from nozzles in the drill bit. The drilling mud, through its density and pressure, controls pressure in the well and cools the bit. The mud also removes formation cuttings from the well as it is circulated back to the vessel. Traditionally, the mud exiting the well is routed through an annulus between the drill string and riser. However, as well control depends at least in part on the column of fluid in the riser, the effects of corrective action in response to a well kick or other anomaly can be delayed.

Fluid lift systems have been deployed subsea for pressurizing the drilling mud exiting the wellbore. Piping systems outside of the riser carry the mud pressurized by the subsea lift systems. The lift systems include pumps disposed proximate the wellhead, which reduce the time for well control actions to take effect.

SUMMARY OF THE INVENTION

In an example, disclosed herein is a method of lifting drilling mud from a subsea wellbore that includes directing an inlet flow of fluid to mud pumps that are disposed subsea, controlling portions of the inlet flow of fluid to individual mud pumps with inlet valves, and opening a one of the inlet valves while closing another one of the inlet valves. Timing the opening and closing of the selected inlet valves keeps individual mud pumps respectively associated with the one of the inlet valves, and the another one of the inlet valves are at the same time in communication with the inlet flow of fluid. This also enables a flow rate of the inlet flow of fluid to remain above a threshold value. The inlet flow of fluid can be drilling mud from the subsea wellbore, and opening and closing of the inlet valves is staggered to maintain the flow rate of the inlet flow of fluid at a substantially constant value. In an alternative, the inlet flow of fluid is water for driving the mud pumps, and opening and closing of the inlet valves is staggered to maintain the flow rate of the inlet flow of fluid at a substantially constant value. The mud pumps can be first, second, and third mud pumps that reciprocate between a mud intake cycle to a mud discharge cycle, and wherein the one of the inlet valves controls flow to the first mud pump and wherein the another one of the inlet valves controls flow to the second mud pump. In this example, the first mud pump changes from the mud intake cycle to the mud discharge cycle when the second pump changes from the mud discharge cycle to the mud intake cycle. Further in this example, the second mud pump changes from the mud intake cycle to the mud discharge cycle when the third pump changes from the mud discharge cycle to the mud intake cycle, and wherein a third inlet valve controls flow to the third mud pump, and wherein the third inlet valve begins to open prior to the another one of the inlet valves closing. Optionally, the another one of the inlet valves is a mud inlet valve, and wherein the mud pumps are driven by selectively flowing pressurized water to water spaces in the mud pumps through water inlet valves, and discharging water from the pumps through water discharge valves. In this example, the method can further include opening a one of the water discharge valves in a one of the mud pumps that is associated with the mud inlet valve.

An alternate method of lifting drilling mud from a subsea wellbore is disclosed herein and that includes directing an inlet flow of drilling mud from the subsea wellbore, controlling a first portion of the inlet flow of drilling mud to a first mud pump with a first mud inlet valve, controlling a second portion of the inlet flow of drilling mud to a second mud pump with a second mud inlet valve, and maintaining a flow rate of the inlet flow of drilling mud above a threshold value by opening the first mud inlet valve prior to closing the second inlet valve. The method can further include controlling a third portion of the inlet flow of drilling mud to a third mud pump with a third mud inlet valve, and opening the second inlet valve prior to closing the third inlet valve. The first mud inlet valve can begin to open at least about 0.5 seconds prior to when the second mud inlet valve is closed. The first and second mud pumps may reciprocatingly discharge mud through first and second mud discharge valves, and wherein pressurized water is selectively delivered to a water side of the first and second mud pumps for discharging mud from the first and second mud pumps.

In another alternative embodiment, disclosed is a method of pumping drilling mud from a subsea wellbore that includes providing first, second and third mud pumps subsea. In this example each pump includes a housing, a water space in the housing, a mud space in the housing, and a membrane in the housing that defines a barrier between the mud space and water space. The method further includes directing first, second, and third portions of a total flow of drilling mud respectively through first, second, and third mud inlet lines and to the first, second and third mud pumps, controlling the first, second, and third portions of the total flow of drilling mud in the first, second, and third mud inlet lines with first, second, and third mud inlet valves that are respectively disposed in the first, second, and third mud inlet lines. Also included with this method are the steps of sequencing the first, second, and third portions of the total flow of drilling mud in the first, second, and third mud inlet lines by closing the first mud inlet valve when opening the second mud inlet valve, selectively directing a flow of pressurized water to the water spaces in the housings of each of the first, second, and third mud pumps to urge drilling mud from the first, second, and third mud pumps, and maintaining the total flow of drilling mud above a threshold value by beginning to open the second inlet valve prior to fully closing the first inlet valve. In an example, the third inlet valve can be opened prior to fully closing the second inlet valve. In another alternative, water can be discharged from the water space of the second mud pump prior to beginning to open the second mud inlet valve.

BRIEF DESCRIPTION OF DRAWINGS

Some of the features and benefits of the present invention having been stated, others will become apparent as the description proceeds when taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a side sectional view of an example of a subsea drilling system having a lift pump assembly and in accordance with the present invention.

FIGS. 2 and 3 are partial side sectional views of an example of a subsea pump for use with the drilling system of FIG. 1 in different pumping modes and in accordance with the present invention.

FIG. 4 is a schematic example of a pumping module for use within the lift pump assembly of FIG. 1 and in accordance with the present invention.

While the invention will be described in connection with the preferred embodiments, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications, and equivalents, as may be included within the spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION OF INVENTION

The method and system of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments are shown. The method and system of the present disclosure may be in many different forms and should not be construed as limited to the illustrated embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey its scope to those skilled in the art. Like numbers refer to like elements throughout.

It is to be further understood that the scope of the present disclosure is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. In the drawings and specification, there have been disclosed illustrative embodiments and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation.

Shown in FIG. 1 is a side partial sectional view of an example embodiment of a drilling system 10 for forming a wellbore 12 subsea. The wellbore 12 intersects a formation 14 that lies beneath the sea floor 16. The wellbore 12 is formed by a rotating bit 18 coupled on an end of a drill string 20 shown extending subsea from a vessel 22 floating on the sea surface 24. The drill string 20 is isolated from seawater by an annular riser 26; whose upper end connects to the vessel 22 and lower end attaches onto a blowout preventer (BOP) 28. The BOP 28 mounts onto a wellhead housing 30 that is set into the sea floor 16 over the wellbore 12. A mud return line 32 is shown having an end connected to the riser 26 above BOP 28, which routes drilling mud exiting the wellbore 12 to a lift pump assembly 34 schematically illustrated subsea. Within the lift pump assembly 34, drilling mud is pressurized for delivery back to the vessel 22 via mud return line 36.

FIG. 2 includes a side sectional view of an example of a pump 38 for use with lift pump assembly 34 (FIG. 1). Pump 38 includes a generally hollow and elliptically shaped pump housing 40. Other shapes for the housing 40 include circular and rectangular, to name a few. An embodiment of a flexible bladder 42 is shown within the housing 40; which partitions the space within the housing 40 to define a mud space 44 on one side of the bladder 42, and a water space 46 on an opposing side of bladder 42. As will be described in more detail below, bladder 42 provides a sealing barrier between mud space 44 and water space 46. In the example of FIG. 2, bladder 42 has a generally elliptical shape and an upper open space 48 formed through a side wall. Upper open space 48 is shown coaxially registered with an opening 50 formed through a side wall of pump housing 40. A disk-like cap 52 bolts onto opening 50, where cap 52 has an axially downward depending lip 53 that coaxially inserts within opening 50 and upper open space 48. A portion of the bladder 42 adjacent its upper open space 48 is wedged between lip 53 and opening 50 to form a sealing surface between bladder 42 and pump housing 40.

A lower open space 54 is formed on a lower end of bladder 42 distal from upper open space 48, which in the example of FIG. 2 is coaxial with upper open space 48. An elliptical bumper 56 is shown coaxially set in the lower open space 54. The bumper 56 includes upper and lower segments 58, 60 coupled together in a clam shell like arrangement, and that respectively seal against upper and lower radial surfaces on the lower open space 54. The combination of sealing engagement of cap 52 and bumper 60 with upper and lower open spaces 42, 54 of bladder 42, effectively define a flow barrier across the opposing surfaces of bladder 42. Further shown in the example of FIG. 2 is an axial rod 62 that attaches coaxially to upper segment 56 and extends axially away from lower segment 58 and through opening 50.

Still referring to FIG. 2, a mud line 64 is shown having an inlet end connected to mud return line 32, and an exit end connected with mud return line 36. A mud inlet valve 66 in mud line 64 provides selective fluid communication from mud return line 32 to a mud lead line 68 shown branching from mud line 64. Lead line 68 attaches to an annular connector 70, which in the illustrated example is bolted onto housing 40. Connector 70 mounts coaxially over an opening 72 shown formed through a sidewall of housing 40 and allows communication between mud space 44 and mud line 64 through lead line 68. A mud exit valve 74 is shown in mud line 64 and provides selective communication between mud line 64 and mud return line 36.

Water may be selectively delivered into water space 46 via a water supply line 76 shown depending from vessel 22 and connecting to lift pump assembly 34 (FIG. 1). Referring back to FIG. 2, a water inlet lead line 78 has an end coupled with water supply line 76 and an opposing end attached with a manifold assembly 80 that mounts onto cap 52. The embodiment of the manifold assembly 80 of FIG. 2 includes a connector 82, mounted onto a free end of a tubular manifold inlet 84, an annular body 86, and a tubular manifold outlet 88, where the inlet and outlet 84, 88 mount on opposing lateral sides of the body 86 and are in fluid communication with body 86. Connector 82 provides a connection point for an end of water inlet lead line 78 to manifold inlet 84 so that lead line 78 is in communication with body 76. A lower end of manifold body 86 couples onto cap 52; the annulus of the manifold body 86 is in fluid communication with water space 46 through a hole in the cap 52 that registers with opening 50. An outlet connector 90 is provided on an end of manifold outlet 88 distal from manifold body 86, which has an end opposite its connection to manifold outlet 88 that is attached to a water outlet lead line 92. On an end opposite from connector 90, water outlet lead line 92 attaches to a water discharge line 94; that as shown in FIG. 1, may optionally provide a flow path directly subsea.

A water inlet valve 96 shown in water inlet lead line 78 provides selective water communication from vessel 22 (FIG. 1) to water space 46 via water inlet lead line 78 and manifold assembly 80. A water outlet valve 98 shown in water outlet lead line 92 selectively provides communication between water space 46 and water discharge line 94 through manifold assembly 80 and water outlet lead line 92.

In one example of operation of pump 38 of FIG. 2 mud inlet valve 66 is in an open configuration, so that mud in mud return line 32 communicates into mud line 64 and mud lead line 68 as indicated by arrow A_(Mi). Further in this example, mud exit valve 74 is in a closed position thereby diverting mud flow into connector 70, through opening 72, and into mud space 44. As illustrated by arrow A_(U), bladder 42 is urged in a direction away from opening 72 by the influx of mud, thereby imparting a force against water within water space 46. In the example, water outlet valve 98 is in an open position, so that water forced from water space 46 by bladder 42 can flow through manifold body 86 and manifold outlet 88 as illustrated by arrow A_(Wo). After exiting manifold outlet 88, water is routed through water outlet lead line 92 and into water discharge line 94.

An example of pressurizing mud within mud space 44 is illustrated in FIG. 3, wherein valves 66, 98 are in a closed position and valves 96, 74 are in an open position. In this example, pressurized water from water supply line 76 is free to enter manifold assembly 80 where it is diverted through opening 50 and into water space 46, thereby urging bladder 42 in a direction shown by arrow A_(D). Injecting pressurized water into the water space 46 urges bladder 42 against the mud, which pressurizes mud in mud space 44 and directs it through opening 72. After exiting opening 72, the pressurized mud flows into lead 68, where it is diverted to mud return line 36 through open mud exit valve 74 as illustrated by arrow A_(Mo). Thus, appropriately pressurizing water into water supply line 76 can sufficiently pressurize mud within mud return line 36 to force mud to flow back to vessel 22 (FIG. 1).

In the examples of FIGS. 2 and 3, valves 66, 74, 78, 98 include an associated actuator for selective opening and closing of the valves 66, 74, 78, 98. Also optionally included is a controller 100 shown in communication with actuators on the valves 66, 74, 78, 98. In one example embodiment, controller 100 communicates commands to the actuators to selectively open and/or close valves 66, 74, 78, 98. In an embodiment, controller 100 includes an information handling system (IHS) that receives or contains instructions to selectively operate valves 66, 74, 78, 98.

FIG. 4 is a schematic illustration of an example of a lift pump assembly 34 having pumps 38A-C arranged in parallel. In this example, and similar to that of FIG. 2, mud flows to pumps 38A-C respectively from mud lines 64A-C that each have an inlet end connected to mud return line 32. Outlet ends of the mud lines 64A-C discharge into mud return line 36. Leads 68A-C respectively communicate mud flow between pumps 38A-C and lines 64A-C, where valves 66A-C, 74A-C regulate flow through lines 64A-C. In similar fashion, water from water supply line 76 flows to pumps 38A-C via water inlet lead lines 78A-C and manifold assemblies 80A-C; and water from pumps 38A-C is delivered to water discharge line 94 via manifold assemblies 80A-C and water outlet lead lines 92A-C. Water to and from pumps 38A-C is controlled respectively by valves 96A-C and 98A-C.

Bladders 42A-C respectively illustrated in pumps 38A-C are oriented to reflect an example of a pump stroke sequence of each pump 38A-C. In the illustrated embodiment, bladder 42A is biased towards manifold 80A and away from lead 68A, so that pump chamber 41A includes a greater volume of mud than water. Pump 38A thus represents an example of a transition from a mud filling stroke to a water filling stroke, which can range from an end of a mud filling stroke to the beginning of a water filling stroke. The illustrated embodiment of pump 38B depicts bladder 42B biased towards lead 68B and away from manifold 80B, which can be a transition from a water filling stroke to a mud filling stroke. Bladder 42C spans generally across a mid-portion of chamber 41C, thus representing pump 38C approximately mid-way through a mud or water filling stroke. Because the filling/discharging strokes of pumps 38A-C of FIG. 4 are staggered, also staggered are the opening and closing of their associated inlet valves 66A-C, 96A-C and exit valves 74A, 98A. For example, inlet valve 66A and outlet valve 98A have just closed or will be closed soon thereafter, whereas inlet valve 66B and outlet valve 98B have just opened or will be opened soon thereafter. Inlet valve 66C and outlet valve 74C are roughly midway through their respective open/closed cycle. An advantage of staggering the sequence of the pumps 38A-C reduces flow rate fluctuations in lines 32, 36, 76, 94, and thus the shock and impulse forces that can occur in these lines when valves suddenly close and reduce the flow rate.

In one example of operation of the lift pump assembly 34 of FIG. 4, the timing of the opening and/or closing of inlet/outlet valves for different pumps 38A-C is adjusted or offset to moderate pressure fluctuations in lines 32, 36, 76, 94 and avoid or minimize the effect known as water hammer. One example of an offset is to not actuate valves from a closed to an open position at the same time other valves, in the same service and the same inlet/outlet side of the pumps 38A-C, are actuated from an open position to a closed position. Instead, a delay can take place between the time instructions are sent to open a closed valve and the time instructions are sent to close an open valve. Example embodiments of the time delay include 0.1 seconds, 0.2 seconds, 0.3 seconds, 0.4 seconds, 0.5 seconds, 0.6 seconds, 0.7 seconds, 0.8 seconds, 0.9 seconds, 1.0 seconds, and any increments of time between these time values. Put another way, a first valve could be opened, or a command sent to initiate opening, at a time in advance of when a second valve is closed. As shown, controller 100 is in communication with valves 66A-C, 74A-C, 96A-C, 98A-C, and can provide instructions to open/close the valves 66A-C, 74A-C, 96A-C, 98A-C, and at designated times.

Still referring to FIG. 4, in an example assuming valves 66A, 98A, 74B, and 96B are open, and valves 74A, 96A, 66B, and 98B are closed, a time delay can take place between the opening of valve 66B and closing of valve 66A so that valve 66B is opened, even if only slightly opened, before valve 66A is closed. Introducing the time delay between the respective opening and closing of valves 66B, 66A provides a destination for the mud flowing in line 32 when valve 66A closes. Instead of an abrupt reduction of flow in line 32, the flow rate of mud in line 32 can be substantially maintained and thus avoid the force impulse that may occur due to an instantaneous flow reduction. In an embodiment, valve 96B is commanded closed with or prior to opening of valve 66B to reduce pressure in water side 46 (FIG. 2) so that mud can flow into mud space 44. Further, examples exist wherein a one of the inlet valves 66A-C is opening, or begins to open, just prior to the closing of any of another one of the inlet valves 66A-C.

The present invention described herein, therefore, is well adapted to carry out the objects and attain the ends and advantages mentioned, as well as others inherent therein. While a presently preferred embodiment of the invention has been given for purposes of disclosure, numerous changes exist in the details of procedures for accomplishing the desired results. These and other similar modifications will readily suggest themselves to those skilled in the art, and are intended to be encompassed within the spirit of the present invention disclosed herein and the scope of the appended claims. 

What is claimed is:
 1. A method of lifting drilling mud from a subsea wellbore comprising: directing an inlet flow of fluid to mud pumps that are disposed subsea; controlling portions of the inlet flow of fluid to individual mud pumps with inlet valves; and opening a one of the inlet valves while closing another one of the inlet valves so that individual mud pumps respectively associated with the one of the inlet valves and the another one of the inlet valves are at the same time in communication with the inlet flow of fluid, and so that a flow rate of the inlet flow of fluid remains above a threshold value.
 2. The method of claim 1, wherein the inlet flow of fluid comprises drilling mud from the subsea wellbore, and opening and closing of the inlet valves is staggered to maintain the flow rate of the inlet flow of fluid at a substantially constant value.
 3. The method of claim 1, wherein the inlet flow of fluid comprises water for driving the mud pumps, and opening and closing of the inlet valves is staggered to maintain the flow rate of the inlet flow of fluid at a substantially constant value.
 4. The method of claim 1, wherein the mud pumps comprise a first, a second, and third mud pumps that reciprocate between a mud intake cycle to a mud discharge cycle, and wherein the one of the inlet valves controls flow to the first mud pump and wherein the another one of the inlet valves controls flow to the second mud pump.
 5. The method of claim 4, wherein the first mud pump changes from the mud intake cycle to the mud discharge cycle when the second pump changes from the mud discharge cycle to the mud intake cycle.
 6. The method of claim 5, wherein the second mud pump changes from the mud intake cycle to the mud discharge cycle when the third pump changes from the mud discharge cycle to the mud intake cycle, and wherein a third inlet valve controls flow to the third mud pump, and wherein the third inlet valve begins to open prior to the another one of the inlet valves closing.
 7. The method of claim 1, wherein the another one of the inlet valves comprises a mud inlet valve, and wherein the mud pumps are driven by selectively flowing pressurized water to water spaces in the mud pumps through water inlet valves, and discharging water from the pumps through water discharge valves, the method further comprising opening a one of the water discharge valves in a one of the mud pumps that is associated with the mud inlet valve.
 8. A method of lifting drilling mud from a subsea wellbore comprising: directing an inlet flow of drilling mud from the subsea wellbore; controlling a first portion of the inlet flow of drilling mud to a first mud pump with a first mud inlet valve; controlling a second portion of the inlet flow of drilling mud to a second mud pump with a second mud inlet valve; and maintaining a flow rate of the inlet flow of drilling mud above a threshold value by opening the first mud inlet valve prior to closing the second inlet valve.
 9. The method of claim 8, further comprising controlling a third portion of the inlet flow of drilling mud to a third mud pump with a third mud inlet valve, and opening the second inlet valve prior to closing the third inlet valve.
 10. The method of claim 8, wherein the first mud inlet valve begins to open at least about 0.5 seconds prior to when the second mud inlet valve is closed.
 11. The method of claim 8, wherein the first and second mud pumps reciprocatingly discharge mud through first and second mud discharge valves, and wherein pressurized water is selectively delivered to a water side of the first and second mud pumps for discharging mud from the first and second mud pumps.
 12. A method of pumping drilling mud from a subsea wellbore comprising: providing first, second and third mud pumps subsea, and that each comprise a housing, a water space in the housing, a mud space in the housing, and a membrane in the housing that defines a barrier between the mud space and water space; directing first, second, and third portions of a total flow of drilling mud respectively through first, second, and third mud inlet lines and to the first, second and third mud pumps; controlling the first, second, and third portions of the total flow of drilling mud in the first, second, and third mud inlet lines with first, second, and third mud inlet valves that are respectively disposed in the first, second, and third mud inlet lines; sequencing the first, second, and third portions of the total flow of drilling mud in the first, second, and third mud inlet lines by closing the first mud inlet valve when opening the second mud inlet valve; selectively directing a flow of pressurized water to the water spaces in the housings of each of the first, second, and third mud pumps to urge drilling mud from the first, second, and third mud pumps; and maintaining the total flow of drilling mud above a threshold value by beginning to open the second inlet valve prior to fully closing the first inlet valve.
 13. The method of claim 12, further comprising beginning to open the third inlet valve prior to fully closing the second inlet valve.
 14. The method of claim 12, further comprising discharging water from the water space of the second mud pump prior to beginning to open the second mud inlet valve. 